Display device

ABSTRACT

A display device for a motor vehicle is proposed, which is used to display a virtual image on the windshield of a motor vehicle. The image is displayed by way of an image-forming unit which is arranged in an upper area of the windshield or in a region of the vehicle roof. The generated image is guided via a first aspherical mirror and a second aspherical mirror onto the windshield.

FIELD OF THE INVENTION

The present invention relates to a display device.

BACKGROUND INFORMATION

From U.S. Pat. No. 5,414,439, a display device in a motor vehicle isalready known in which an image, picked up by an infrared camera, can beprojected by a display, arranged in the dashboard, via an asphericalmirror, likewise arranged in the dashboard, onto the windshield. Avirtual image, which is visible for a driver in the vehicle, appears onthe windshield. In this case, both the display and the aspherical mirrormust be disposed in the dashboard. In addition, an opening must beprovided in the dashboard for the light which is reflected by theaspherical mirror to the windshield and which is necessary for an imagerepresentation.

SUMMARY OF THE INVENTION

In contrast, the display device of the present invention has theadvantage that a display device for a virtual image can be implementedin a space-saving manner in a vehicle; for because an image-forming unitis arranged in the region of the vehicle roof or in an upper region ofthe windshield, an arrangement of optical elements within the dashboardcan be dispensed with to the greatest extent possible. In particular, itis not necessary to provide a light path within the dashboard.Therefore, it is possible to dispense with a corresponding opening inthe region of the dashboard. Consequently, due to the reduced spacerequirements, costs when constructing the display device can be lowered.It is also possible to retrofit a display device of the presentinvention on a vehicle which is not designed for such a display deviceby its manufacturer and in which no place is provided for a light pathin the dashboard. In addition, temperature problems can be avoided whichcan occur with an arrangement of an image-forming unit in the dashboard,since the dashboard can generally heat up particularly strongly due todirect exposure to sunlight.

It is particularly advantageous to arrange the second aspherical mirroron the dashboard in a manner that the mirror can be covered. Soiling ordamage of the mirror can thereby be avoided.

Furthermore, it is advantageous to design the first or the secondaspherical mirror to be adjustable by motor. Such an adjustment permitsadaptation of the alignment of the first and/or the second asphericalmirror to a sitting position of a driver, so that the position of thevirtual image can be optimally adjusted.

It is also advantageous to carry out this adjustment via an operatingelement, so that unnecessary touching of the mirror, and soilingpossibly associated with it, can be avoided.

It is furthermore advantageous to design the image-forming unit as aliquid-crystal cell having a backlighting, since in this way, theimage-forming unit can be implemented particularly inexpensively.

Another advantage is for the windshield to be wedge-shaped. It isthereby possible to avoid double images in the projection which areformed because, in a windshield made of safety glass, multiplerefraction can take place at the individual glass layers of the safetyglass. The wedge-shaped design makes it possible for these double imagesto fall on one another, and only one image is visible for an observer.

Moreover, it is advantageous to integrate the image-forming unit or thefirst aspherical mirror into an interior mirror module. Installationexpenditure can thereby be further reduced, since only the interiormirror module is arranged on the windshield or on the vehicle roof. Inthis context, the image-forming unit may also be covered for a user bythe interior mirror, and a possible disturbance to the user by avisible, image-forming unit is avoided.

It is further advantageous to cover the mirror with a foil, whichreduces the visibility of the mirror without at the same timesubstantially influencing the reflection properties of the mirror. Bythis, a glare, e.g. by sunlight which falls on the second asphericalmirror, can be avoided to the greatest extent possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first exemplary embodiment of the display deviceaccording to the present invention in a motor vehicle.

FIG. 2 shows a design of an image-forming unit having a liquid-crystalcell.

FIG. 3 shows another exemplary embodiment of a display device accordingto the present invention.

FIG. 4 shows a further exemplary embodiment of a display device of thepresent invention.

DETAILED DESCRIPTION

FIG. 1 shows the front area of a passenger compartment of a motorvehicle in a longitudinal cross-section. An image-forming unit 2 isarranged on a windshield 1 of the vehicle. Image-forming unit 2 ispositioned on the windshield near to a vehicle roof 3 and is connectedto a camera 5 via a data connection 4, the entire connection not beingshown in the Figure, but rather being indicated by arrows. A cover 6 isarranged on vehicle roof 3. Cover 6 has an indentation 7 in which afirst aspherical mirror 8 is arranged. Below windshield 1 is thedashboard whose top side 10 adjoins windshield 1. A second asphericalmirror 11 is situated on top side 10 of the dashboard. The position ofsecond aspherical mirror 11 can be changed by a first motor 12 and asecond motor 13. Both first motor 12 and second motor 13 are controlledby a control unit 14. Control unit 14 can be influenced by a user via anoperating control element 15. For example, operating control element 15has rotary knobs and/or push buttons. Control unit 14 is also connectedto an ignition lock 16. A data connection, particularly for thebrightness control of the virtual image displayed on windshield 1, fromcontrol unit 14 to image-forming unit 2 is not shown in the figure. Acover flap 17 is arranged next to second aspherical mirror 11. Coverflap 17 can be folded over second aspherical mirror 11, and to this end,is movable by a third motor 18 which is also controlled by control unit14. Second aspherical mirror 11 is situated behind a steering wheel 19on the side of steering wheel 19 facing away from a driver of thevehicle. Ignition lock 16 and operating control element 15 arepreferably arranged next to steering wheel 19. Light beams running fromimage-forming unit 2 are guided via first aspherical mirror 8 to secondaspherical mirror 11, from there onto windshield 1, from which in turnthey are guided to the eye of an observer located in front of steeringwheel 19. A beam path 20 between the named elements is drawn in, the eyeof the observer being indicated by an arrow 22 at beam path 20. Due toreflections on windshield 1, a virtual image is formed which anobserver, preferably the driver, can perceive.

In the exemplary embodiment shown in FIG. 1, image-forming unit 2 isarranged on windshield 1 near the vehicle roof. It is also possible tointegrate image-forming unit 2 into vehicle roof 3. The image is formedin image-forming unit 2, for example, using a backlit liquid-crystalcell. An exemplary embodiment for this is shown in FIG. 2. Image-formingunit 2 is provided with an opening 34, behind which a liquid-crystalcell 33 is arranged. Liquid-crystal cell 33 has segments which can beelectrically controlled individually and whose optical transmission canbe influenced by the electrical control. The individual segments are notshown in FIG. 2. In one preferred exemplary embodiment, liquid-crystalcell 33 has a screen diagonal of 1.3 inches. A diffuser 32 is arrangedon the side of liquid-crystal cell 33 facing away from opening 34.Located on the side of diffuser 32 facing away from opening 34 is anarrangement of light-emitting diodes 31 which are preferably arranged ona printed circuit board 30. A voltage supply of light-emitting diodes 31is not marked in in FIG. 2. For example, instead of light-emittingdiodes 31, a backlighting using incandescent lamps, glow lamps orcold-cathode fluorescent lamps is possible. The light generated bylight-emitting diodes 31 strikes on diffuser 32 which scatters theincident light and thus contributes to a homogenous backlighting ofliquid-crystal cell 33. At this point, an image formation is possible bythe control of individual segments of liquid-crystal cell 33. In sodoing, various image colors are possible as a function of the color oflight-emitting diodes 31; for example, when working with redlight-emitting diodes, the image is composed of various shades of red,while white light-emitting diodes result in a representation in shadesof gray.

The light of the image generated by liquid-crystal cell 33 emerges fromopening 34, runs along beam path 20 and strikes first of all on firstaspherical mirror 8, as shown in FIG. 1. First aspherical mirror 8 isconcave-curved on its side facing image-forming unit 2, and has a focaldistance in a range from 50 mm to 120 mm. In one preferred exemplaryembodiment, first aspherical mirror 8 has a focal distance of 90 mm.First aspherical mirror 8 is, for example, concave in the form of asegment of a spherical surface, an ellipsoid of revolution or acylindrical surface. First aspherical mirror 8 is arranged inindentation 7 of cover 6 of vehicle roof 3 using a holding device 21.First aspherical mirror 8 is adjusted during installation of the displaydevice in the vehicle, the position of first aspherical mirror 8 inindentation 7 being so adjusted that an optimal image representationresults on windshield 1. However, in an exemplary embodiment not shownin the drawing, it is also possible to provide a motor control or amanual adjusting device at first aspherical mirror 8 which permits areadjustment. The light is guided along beam path 20 to secondaspherical mirror 11. Like the first aspherical mirror, secondaspherical mirror 11 is likewise concave and has a focal distancebetween 300 mm and 800 mm. In one preferred exemplary embodiment, thefocal distance is 430 mm. Second aspherical mirror 11 is adjustablymounted, so that using a first motor 12 and a second motor 13, themirror is adjustable about two axes running perpendicular to one anotherin a mirror plane. An implementation possibility not shown in the Figureis, for example, to support second aspherical mirror 11 at these axes ofrotation on top side 10 of the dashboard, and to connect first motor 12to the one, and second motor 13 to the other axis. Beam path 20, whichruns from the second aspherical mirror to windshield 1, is changed by anadjustment of second aspherical mirror 11. The position of the virtualimage, which is visible for an observer on windshield 1, is therebyalterable. In this way, it is possible, for example, to adjust theposition of the image to the seat position of a driver and to his/herbody size. To this end, using operating control element 15 which isconnected to control unit 14, that in turn is connected to first motor12 and to second motor 13, the driver can activate first motor 12 andsecond motor 13, respectively, and in this way adjust second asphericalmirror 11. Arranged next to second aspherical mirror 11 is a cover flap17 which, in a first state, covers second aspherical mirror 1 1, and ina second state, clears. To that end, in a first exemplary embodiment,cover flap 17 can be folded over second aspherical mirror 11 by thirdmotor 18, which is likewise connected to control unit 14, the cover flapbeing supported on an axle. Furthermore, in another exemplaryembodiment, it is possible to slide cover flap 17 over second asphericalmirror 11 with the aid of third motor 18.

Particularly when the vehicle is stationary, the display device is notneeded. Therefore, control unit 14 is connected to ignition lock 16. Ifthe vehicle is switched off, then third motor 18 is activated and secondaspherical mirror 11 is covered by cover flap 17. When the vehicle isstarted again, control unit 14 detects an actuation of ignition lock 16and the third motor is activated, so that second aspherical mirror 11 iscleared again by cover flap 17.

Camera 5 is preferably designed as an infrared camera and is used duringpoor visibility, for example, in fog, to pick up an image of the roadcourse and, from that, to generate video information which istransmitted via data connection 4 to image-forming unit 2 for display onwindshield 1. For that purpose, camera 5 is preferably arranged in afront area of the vehicle, for example, in the area of a radiator grilleor a headlight.

FIG. 3 shows another exemplary embodiment of the display deviceaccording to the present invention. Here and in the following, identicalreference numerals also designate identical elements. Image-forming unit2 is arranged on an interior mirror 40. Interior mirror 40 is in turnconnected to a housing 43 via a holder 41. Interior mirror 40, holder 41and housing 43 form an interior mirror module. An electrical connectionto image-forming unit 2 runs via holder 41. Housing 43 is integratedinto vehicle roof 3, preferably in a U-profile which, for reasons ofbody technology, is present there in a great number of vehicles, andthus offers place for housing 43 without housing 43 extending into thepassenger compartment. First aspherical mirror 8 is arranged outside onhousing 43. Interior mirror 40 hides image-forming unit 2 to thegreatest extent possible from an observer who is located in front ofsteering wheel 19. For example, data connection 4 to image-forming unit2 runs along side piece 44 which is arranged between the windshield anda side window 46. Second aspherical mirror 11 in the exemplaryembodiment is rectangular. In one preferred exemplary embodiment, thehorizontal extension, thus parallel to the windshield, lies atapproximately 250 mm, in an extension direction perpendicular to thewindshield, lies at 90 mm. First aspherical mirror 8 has an area of 100mm by 40 mm. Cover flap 17 can be folded over second aspherical mirror11.

A further exemplary embodiment is shown in FIG. 4. In this exemplaryembodiment, a second aspherical mirror 50 is drawn in. Second asphericalmirror 50 is designed so that it itself is capable of folding, an axisof rotation running along a longitudinal side 52 of second asphericalmirror 50. Disposed next to aspherical mirror 50 is a depression 51 intowhich second aspherical mirror 50 is able to fold. The back side of thesecond aspherical mirror, thus the side opposite the mirror side, iscovered with a plastic that preferably is made of the same material astop side 10 of the dashboard, so that the back side of the secondaspherical mirror stands out as little as possible from top side 10 ofthe dashboard. In this exemplary embodiment, an adjustment of secondaspherical mirror 50 with respect to the position of the virtual imageon windshield I can take place about the axis running along longitudinalside 52. In addition, this axle itself can be designed to be inclinablein a direction perpendicular to its axial direction.

A possible glare for a driver can be avoided by an additional cover,preferably by a cover foil arranged on second aspherical mirror 11 and50, respectively. For that purpose, it is possible, for example, toarrange a polarizer foil on second aspherical mirror 11 or 50.Particularly when using a liquid-crystal cell or a coherent lightsource, e.g. a laser, in image-forming unit 2, the light striking secondaspherical mirror 11 or 50 via first aspherical mirror 8 is polarized.If a polarizer, which is arranged in such a way that it exhibits anabsorption minimum for the light of image-forming unit 2, is nowdisposed on second aspherical mirror 11, 50, then only a minimumbrightness loss occurs in the reflection, preferably an anti-reflectioncoating additionally being applied on the polarizer. Thus at least halfof environmental light, which generally exhibits a uniform distributionover all polarization directions, is absorbed, and a possible glareeffect is reduced without the brightness of the virtual image projectedonto windshield I being substantially impaired thereby. Furthermore, itis also possible to arrange shutter foils on second aspherical mirror11, thus foils which allow a light to come in or exit only at apreferred angle of incidence or angle of reflection, this effect beingachieved, for example, by a mask pattern integrated into the foil. Alight leak from second aspherical mirror 11, 50 to an observer locatedin front of steering wheel 19 is thereby sharply reduced, as well.

Operating control element 15 is further used to adjust the imagebrightness. This is effected, for example, by increasing or decreasingan operating voltage for light-emitting diodes 31 located inimage-forming unit 2, to thus increase or decrease the brightness oflight-emitting diodes 31. In addition to the indicated design ofimage-forming unit 2 as a liquid-crystal cell 33 having a backlighting,it is also possible to design image-forming unit 2 as a laser display, amicro-mirror display, a vacuum fluorescent display or a plasma display.While the vacuum fluorescent display and the plasma display are luminousdisplays themselves, for which a backlighting is unnecessary, in thecase of the two other specific embodiments, the laser display and themicro-mirror display, a preferably coherent light source, e.g. a laserunit, can be arranged in image-forming unit 2. The image is now formedeither by an activation of the laser unit or by an activation of themicro-mirrors.

Windshield 1 is preferably wedge-shaped in that it is thicker in anupper region allocated to vehicle roof 3, and tapers in the direction oftop side 10 of the dashboard. The tapering is achieved in that two glasspanes which form the safety glass of the windshield are inserted so thatthey are not quite parallel, but rather have a greater clearance in anupper region of the windshield. Given a reflection of the light issuingfrom second aspherical mirror 11, 50 onto windshield 1, a reflectionoccurs at the two glass panes of windshield 1. Because of thewedge-shaped design, the virtual images resulting due to the reflectioncoincide for an observer. A windshield vapor deposition which, forexample, prevents the reflection on a pane, is now no longer necessary.

What is claimed is:
 1. A display device in a motor vehicle, comprising:an image-forming unit arranged in one of an area of a vehicle roof andin an upper region of a windshield of the motor vehicle; a firstaspherical mirror arranged in the area of the vehicle roof; and a secondaspherical mirror arranged in a region of a dashboard of the motorvehicle, wherein: light emitted by the image-forming unit istransmittable to the first aspherical mirror, light from the firstaspherical mirror is projectable onto the second aspherical mirror,light from the second aspherical mirror is projectable onto thewindshield, and a virtual image is able to be formed on the windshield.2. The display device according to claim 1, wherein: the secondaspherical mirror is arranged on the dashboard in a manner that thesecond aspherical mirror can be covered.
 3. The display device accordingto claim 2, wherein: the second aspherical mirror is arranged on a topside of the dashboard.
 4. The display device according to claim 1,further comprising: at least one motor for performing a motor-adjustmenton at least one of the first aspherical mirror and the second asphericalmirror.
 5. The display device according to claim 1, further comprising:an operating control element arranged in the motor vehicle and foradjusting at least one of the first aspherical mirror, the secondaspherical mirror, and an image brightness of the virtual image formedonto the windshield.
 6. The display device according to claim 1,wherein: the first aspherical mirror has a focal distance in a rangefrom 50 mm to 120 mm, and the second aspherical mirror has a focaldistance in a range from 300 mm to 800 mm.
 7. The display deviceaccording to claim 1, wherein: the image-forming unit includes one of abacklit liquid-crystal cell, a laser display, a micro-mirror display, avacuum fluorescent display, and a plasma display.
 8. The display deviceaccording to claim 1, wherein: the windshield is wedge-shaped.
 9. Thedisplay device according to claim 1, wherein: the image-forming unit isarranged on an interior mirror module.
 10. The display device accordingto claim 1, wherein: the first aspherical mirror is arranged on aninterior mirror module.
 11. The display device according to claim 1,wherein: the first aspherical mirror is arranged on a housing at thevehicle roof.
 12. The display device according to claim 1, furthercomprising: a camera arranged on the motor vehicle, wherein: an imagepicked up by the camera is able to be projected as the virtual image onthe windshield.
 13. The display device according to claim 12, wherein:the camera includes an infrared camera.
 14. The display device accordingto claim 1, further comprising: a foil for covering the secondaspherical mirror and for reducing a visibility of second asphericalmirror.